At the start of Thucydides’ history of the Peloponnesian War, he provides a simple explanation as to why the conflict between Sparta and the Athenian Empire broke out. He writes, “what made war inevitable was the growth of Athenian power and the fear which this caused in Sparta”. Despite the tailored nature of this statement to the Peloponnesian War, its analysis of the start of wars serves as a pertinent warning from history.

Professor Graham Allison of Harvard has made waves in the USA with his work on how this “Thucydides’ Trap” relates to us now. In recent years, an existential threat to the West has developed, though remaining hidden in plain sight. Across the globe, outposts of Chinese imperialism and aggression are surfacing. Indeed, striking parallels are present between the power dynamic between Athens and Sparta, and China and the West.

Yet war did not become inevitable for Athens and Sparta until the last moment, and it is not inevitable now. It took not only Athenian growth but Spartan fear too in order to create a war. The key to peace and security lies in a capable response to the rapid rise of a rival. This analysis is as applicable to modern international relations as it was at the time of the Peloponnesian War. A careful response is required in order to protect the West from the advance of a force which scorns freedom.

Despite what President Trump seeks to prove, erratic economic nationalism is not strength. Rather than the confused nativism of the Trump Doctrine – at one time attacking China, at another cosying up to Xi – a stable and consistent method is required. With American politics and economic priorities in disarray, carrying the mantle of the “leader of the free world” must fall to another power in order to protect Western values. That power is Britain.

This is the role that Margaret Thatcher reminded the nation of in 1976 when she said that “we in Britain cannot opt out of the world”. That belief stemmed from a conviction that the United Kingdom had been appointed a duty in the post-war world. Acting as the bridge between Europe and America, Britain remained a diplomatic power in defence of liberty even after her empire was long gone. Mrs Thatcher understood that what was at stake in the Cold War was individual freedom. And it is the spread of freedom that must once more be our primary cause in the world.

Because China has acted with stunning consistency against freedom. Its “Belt and Road” scheme of infrastructure is a vast economic weapon designed to spread Chinese influence and rule over the globe by entrapping poor and helpless nations in the shackles of debt.

Sri Lanka learned the hard way: a port paid for with Chinese loans fell into Chinese hands when the Sri Lankans could not pay their debts. It became a convenient outpost of Chinese influence. This is not a one-off, but part of a chain of debt strangling the developing world. Just as the Athenians of Thucydides’ time used the naval alliance of the Delian League to draw tribute from lesser city-states and build an empire, so the Chinese are using trade and infrastructure to spread their tyranny and make the 21st century a Chinese one.

Within China, a chilling police state has taken root. The Chinese paranoia over the Muslim Uighurs of the Xinjiang province in the north-west of the country has led to 80 per cent of the urban adult population there being rounded up, with families separated and citizens hit by crippling travel restrictions.

The Uighurs are feeling the full force of a state which has mastered digital profiling. Why? Because Xinjiang is a crucial area for the Belt and Road Initiative. The Chinese will stop at nothing to extend their power, and wherever that power spreads, freedom dies. In China, there is no freedom of speech, no free press, no true free trade, no true free market, no privacy, and no democracy. The values for which the West has long fought, the values that drive the neoliberal worldview – the values of decency and human dignity – will perish if we do not act now.

Britain and the rest of the West find themselves facing two monstrous futures. On one side of the ever-teetering scales is Thucydides’ Trap, threatening to engulf the world in destructive war if we are reckless. On the other side, if we do not act, is the subjugation of the world under the Chinese jackboot and the slide of the globe away from liberalism towards brutal totalitarianism.

If Britain wants to help shake the West from its inertia and create the possibility of a future relationship with China which keeps the global peace and stops the steady advance of tyranny, there are a number of obvious steps.

For a start, our defence spending must increase. Diplomacy is built on strength, and strength is built on defence. We must increase the size of our armed forces and keep up with changes in technology, and this means significant rises in our defence budget year on year. Not only can we not expect other nations to listen to us if we take a lacklustre attitude to our defence expenditure but we risk the massive blow of losing our place as America’s “partner of choice”, to France. If we wish to wield influence over China, defence spending is the place to begin.

The Government would also have to ignore the parochial siren song of those who want to slash our aid budget. A skilful and considerate use of UK aid money spreads Western influence and freedom abroad and is a bulwark against the advance of China’s insidious loans. Those who argue that the money is better spent at home miss the point entirely – aid does not just benefit the recipient.

Finally, any global response to China must start at home. Britain must no longer be seduced by projects such as Hinkley Point C, a project which gives China influence and power over us. Scrutiny of Chinese investment and influence in the UK must increase, as a matter of national security.

If we follow these steps and prepare ourselves for the fight, Britain will be well placed to spearhead and initiate a Western response to China which allows us to negotiate properly, roll back the progress of Chinese power in poor countries, and come to the kind of mutually beneficial agreement which will steer the world away from the waiting jaws of Thucydides’ Trap. China has much to gain from toning down its aggression – however much it has to win from its expansionism, it can win even more from the security of a new world consensus.

Indeed, as we move quickly towards our exit from the European Union, many politicians talk of “Global Britain”. Brexit or no Brexit, a global Britain is one we must all get behind. Because if we seize the day on China, we will not just be doing our duty, we will also gain more respect from our friends and foes, strengthen our diplomatic power, and show any doubters that the British commitment to freedom is strong and unconquerable.

Despite the current internal divisions hurting the West, we must awake to the existential threat knocking on our door. We must be guided by the words of that stalwart defender of freedom, Ronald Reagan, who warned: “Freedom is never more than one generation away from extinction. We didn’t pass it on to our children in the bloodstream. It must be fought for, protected, and handed on for them to do the same”. That is the challenge, and it is one that Britain must embrace.